This invention relates generally to systems and methods for operating downhole apparatus. The invention relates more particularly, but not by way of limitation, to a system and method for selectively actuating multiple downhole tools based on the amount of pressure applied to the annulus of an oil or gas well.
During the drilling, completing and producing of an oil or gas well, various apparatus typically need to be lowered into the well for one purpose or another. For example, a formation tester valve and a circulation valve are devices that are used to conduct a drill stem test. The tester valve is repeatedly opened and closed to allow and prevent oil or gas flow from the well so that the pressure in the well can be checked under such flow and shut-in conditions. After the desired cycling of the tester valve has been completed, the circulation valve is opened to allow fluid to be circulated between the surface and well.
Typically such downhole apparatus do not need to be operated until they are at a desired depth in the well. Thus, there is the need for some way to operate such apparatus when they are down in the well. Although such apparatus can be automatically self-controlled so that they perform desired operations at predetermined times, many such apparatus need to perform their functions at times that cannot be predetermined. For these apparatus, there needs to be some way of communicating from the surface a command signal that will initiate or otherwise affect operation of the apparatus.
This need for surface to downhole communication has been well recognized in the oil and gas industry, and many techniques have been developed For example, an apparatus can be lowered into a well on an electrically conductive cable, known as a wireline, so that electrical signals can be transferred between the surface and the apparatus down in the well. As other examples, an apparatus can be lowered into a well as part of a pipe string along which acoustic or electromagnetic signals can be sent. As a further example, pressure signals can be sent through fluid in a pipe string or in an annulus around the pipe string. A specific example of a downhole tool that responds to external annulus pressure and internal pressurized gas is shown in U.S. Pat. Nos. 4,633,952 and 4,711,305 to Ringgenberg.